Added support for DESC and NULLS FIRST/LAST to index keys

Fixes issue #3
Function get_index_keys() renamed to get_order_by()

It was a FIXME item in the source. Reasonably so.
Added support for COLLATE to index keys
Added pg_repack runs to check the get_order_by definitions work
Merge remote-tracking branch 'piro/issue-3'

Conflicts:
	bin/expected/repack.out
	bin/sql/repack.sql
Test fixed after change 66ae2f33a74943d75e6049603fa07eacf46fa1be